docs/library/esp.rst: Document the osdebug function.

docs/library/esp.rst

@@ -62,6 +62,21 @@ Functions
 
 .. function:: flash_erase(sector_no)
 
+.. function:: osdebug(level)
+
+    Turn esp os debugging messages on or off.
+
+    The *level* parameter sets the threshold for the log messages for all esp components.
+    The log levels are defined as constants:
+
+        * ``LOG_NONE`` -- No log output
+        * ``LOG_ERROR`` -- Critical errors, software module can not recover on its own
+        * ``LOG_WARN`` -- Error conditions from which recovery measures have been taken
+        * ``LOG_INFO`` -- Information messages which describe normal flow of events
+        * ``LOG_DEBUG`` -- Extra information which is not necessary for normal use (values, pointers, sizes, etc)
+        * ``LOG_VERBOSE`` -- Bigger chunks of debugging information, or frequent messages
+          which can potentially flood the output
+
 .. function:: set_native_code_location(start, length)
 
     **Note**: ESP8266 only